Ceramic thermal barrier coatings are well known for protecting metal or ceramic matrix composite materials from oxidation and corrosion in a gas turbine environment. One type of thermal barrier coating used to protect a nickel-based or cobalt-based superalloy component includes an MCrAIY bond coat, where M is iron, nickel, cobalt or a combination thereof, that is oxidized in-situ to form an alumina layer for receiving a top coat of yttria stabilized zirconia (YSZ). The YSZ coating is commonly applied by electron beam physical vapor deposition (EB-PVD) to form a columnar structure, or by air plasm spraying (APS) to form a planar structure consisting of a plurality of overlapping splats of material. Within each frozen splat of material in an APS coating, the microstructure of the material may have a columnar structure.
U.S. Pat. No. 6,689,487 issued on Feb. 10, 2004 describes one such thermal barrier coating applied by an EB-PVD process. That EB-PVD process is controlled so that the coating includes primary columnar grains extending transversely from the substrate surface and secondary columnar grains (feathers) extending laterally from the primary columnar grains.